Metallocene compounds, i.e., compounds having a transition metal atom coordinated with a multidentate compound containing a π-electron donating group such as an unsubstituted or substituted cycloalkadienyl group, for example, an unsubstituted or substituted cyclopentadienyl group, an unsubstituted or substituted indenyl group, an unsubstituted or substituted tetrahydroindenyl group, and an unsubstituted or substituted fluorenyl group have been partly used in the place of the Ziegler-Natta catalyst which has been heretofore used for the polymerization of an olefin.
Particularly in recent years, various metallocene compounds showing increasingly high olefin polymerization activity per mol of a transition metal atom have been proposed. For example, a chiral metallocene compound which has a transition metal atom coordinated with a multidentate compound having two substituted cycloalkadienyl groups cross-linked with a divalent linking group has been proposed (J. Am. Soc. 1998, 120, 11316-11322). It has been reported that α-olefin polymers of not less than three carbon atoms, particularly a propylene polymer, polymerized by the use of this compound as a catalyst has a high stereoregularity.
Further, the development of metallocene compounds showing a high polymerization activity in the polymerization of olefins is being continued. Then, various metallocene compounds incorporating therein heteroatoms as a constituent for forming a substituent to be bonded to a cycloalkadienyl ring or forming a cycloalkadiene ring itself have been proposed.
U.S. Pat. No. 5,585,509 (DE 4406963, JP-A-7-258282), for example, discloses a metallocene compound having an indenyl group in which a hydrogen at the 2-position of the indenyl group is replaced by a saturated group containing a heteroatom such as a nitrogen atom, a phosphorus atom, an arsenic atom, an antimony atom and a bismuth atom, specifically a metallocene compound obtained by cross-linking two 2-pyrrolidino-1-indene with a divalent linking group and coordinating it to a transition metal atom.
Then, JP-A-8-183814 discloses a metallocene compound having an indenyl group in which a hydrogen at the 4-position of the indenyl group is replaced by a 1-pyrrolyl group, a 1-indolyl group, etc., specifically a chiral metallocene compound obtained by cross-linking two 4-(1-indolyl)-2-methyl-indenes with a divalent linking group and coordinating it to a transition metal atom.
Further, J. Am. Chem. Soc. 1998, 120, 10786-10787 discloses a metallocene compound obtained by cross-linking with a divalent linking group two heteroatom-containing cycloalkadienes, each having a thiophene ring or a pyrrol ring condensed with a cyclopentadiene ring, and coordinating it to a transition metal atom.
U.S. Pat. No. 5,840,947 (DE 19517851, JP-A-8-333379) discloses a metallocene compound having a pyridyl group, quinolyl group, etc. as a substituent.
These metallocene compounds generally have mainly been developed with a view to producing a high molecular weight olefin polymer and controlling a stereoregularity of the produced olefin polymer to a high degree.
When a propylene/ethylene copolymer is produced by using a metallocene catalyst, however, the molecular weight of the produced copolymer is generally lowered to no small extent in proportion to the amount of ethylene in the copolymer as compared with that of a propylene homopolymer (T. Sugano, SPO '99, 31-53 (1999). Even in the production of such a copolymer, therefore, development of a metallocene compound capable of producing the copolymer having a high molecular weight has been desired.
As the olefin polymer having a controlled stereoregularity, JP-A-10-273507 has reported a highly stereoregular propylene polymer, wherein (A) the isotactic triad ratio of the propylene unit chain part formed by head-tail bonds is not less than 97% as determined by the method of 13C-NMR nuclear magnetic resonance spectrum analysis (13C-NMR); (B) the proportion of the propylene units originating from 2,1-insertion of the propylene monomer in the whole propylene units is in the range of 0.5-2.0 mol % and the proportion of the propylene units originating from 1,3-insertion of the propylene monomer is in the range of 0.06-0.4 mol %, as determined by the 13C-NMR; and (C) the weight average molecular weight, Mw is in the range of 10,000-1,000,000 as determined by the gel permeation chromatography (GPC).
JP-A-11-171925 has reported a highly stereoregular propylene polymer, wherein (A) the isotactic triad ratio of the propylene unit chain part formed by head-tail bonds is not less than 98% as determined by the 13C-NMR; (B) the proportion of the propylene units originating from 2,1-insertion of the propylene monomer in the whole propylene units is not more than 0.03 mol % and the proportion of the propylene units originating from 1,3-insertion of the propylene monomer is not less than 0.06 mol %, as determined by the 13C-NMR; (C) the weight average molecular weight is in the range of 10,000-1,000,000; and (D) the melting point is not lower than 160° C.
Then, JP-A-7-145212 has reported a propylene polymer having a high stiffness and a high heat resistance, wherein (A) the triad tacticity of the propylene unit chain part formed by head-tail bonds is not less than 90.0% as determined by the 13C-NMR; (B) the proportion of the propylene units originating from 2,1-insertion of the propylene monomer in the whole propylene units is not less than 0.7 mol % and the proportion of the propylene units originating from 1,3-insertion of the propylene monomer is not more than 0.05 mol %, as determined by the 13C-NMR; and (C) the intrinsic viscosity is in the range of 0.1-12 dl/g as determined in decalin at 135° C.
Further, JP-A-7-149832 has reported a propylene copolymer having a high stiffness and a high heat resistance, wherein (A) the content of a propylene unit is in the range of 95-99.5 mol % and that of an ethylene unit is in the range of 0.5-5 mol %; (B) the triad tacticity of the propylene unit chain part formed by head-tail bonds is not less than 90.0% as determined by the 13C-NMR; (C) the proportion of the propylene units originating from 2,1-insertion of the propylene monomer in the whole propylene units is not less than 0.5 mol % and the proportion of the propylene units originating from 1,3-insertion of the propylene monomer is not more than 0.05 mol %, as determined by the 13C-NMR; and (D) the intrinsic viscosity is in the range of 0.1-12 dl/g as determined in decalin at 135° C.